The major objective of the research project is to determine the mechanisms of control responsible for the production of fetal hemoglobin (HbF) and adult hemoglobin (HbA) in the baboon, Papio cynocephalus. This species was chosen because it provides an excellent experimental model for elucidation for HbF synthesis. The specific aims of the project are: 1. To determine the factors underlying the switch from adult hemoglobin synthesis to fetal hemoglobin synthesis following acute hypoxic stress in vivo, 2. To determine the minimal amount of hypoxic stress required to induce F-cell synthesis, 3. To detemine the erythrocyte precursor cell stages which can respond to hypoxic stress by synthesizing HbF, 4. To determine the factors underlying the switch from HbA synthesis to HbF synthesis which occurs during erythroid cell culture. 5. To determine the factors underlying the switch from HbF synthesis to HbA synthesis which occurs during fetal and neonatal development.